The phagocytic activity of human first trimester extravillous trophoblast

It has been suggested previously that phagocytic activity in the human plac enta is confined to cells of the macrophage lineage. However, earlier studi es were hampered by the paucity and poor viability of cells inherent in pri mary trophoblast cell cultures, contamination by other cell types which the mselves have phagocytic activity, lack of reliable markers of trophoblasts, and by limitations of methods available to demonstrate unequivocally the i nternalization of particulate material. We have overcome these limitations by using: (i) DNA transfection to provide unlimited supplies of pure tropho blast cell lines; (ii) human placental lactogen as a marker unique to troph oblast; and (iii) confocal microscopy to demonstrate unequivocally the intr acellular locality of phagocytosed material. We found that both untransfect ed primary culture extravillous trophoblast cells, as well as the cell line s, had the capacity to phagocytose sheep red blood cells, Staphylococcus au reus and baker's yeast cells, and that this activity was inhibited by cytoc halasin B and by culture at 4 degrees C. Phagocytic activity in trophoblast cells was less avid than that seen in a professional phagocyte. In physiol ogical and pathological situations where tissue remodelling occurs, such as the rapid turnover in the periodontal ligament or during inflammation, epi thelial cells and other cells that are not considered professional phagocyt es actively phagocytose components of the extracellular matrix. We postulat e that phagocytosis by human trophoblasts may play an important role in the extensive tissue remodelling that occurs during trophoblastic invasion of the decidua.